The present invention relates generally to fluid seals, and more particularly, to a specialized seal assembly for retaining a fluid such as a compressed gas within the tubular housing portion of a so-called gas spring, that is, a cylinder unit having a reciprocable piston and operating rod assembly disposed therein and biased by a pressurized gas or the like toward an extended position.
More particularly, the invention relates to a one-piece seal unit having a number of novel features and advantages especially adapting it for use in such application. In another aspect of the invention, the invention relates to the combination of such seal with other elements of a gas spring assembly, and to the method of sealing gas springs of the type just referred to.
Because of the availability of seals which are generally satisfactory for the primary function of sealing gas pressure, certain of the potential advantages of so-called gas springs have been fully utilized. These include the provision of an assembly which may endure substantial preloads for a significant time without loss of spring effectiveness, low cost, relative safety in use, ready replaceability, and compatibility with existing technology.
More importantly, so-called gas springs may be made to include other advantageous features, a principal one of which is the ability, without the use of a large number of parts, to provide both spring and damping actions without adding parts.
Still further, gas spring units have the advantage of being able to receive varying amounts of internal pressure and hence, provide varying spring forces without change of mechanical parts or redesign. In this connection, for example, if a gas spring of a particular size is to exert a force sufficient to offset a ten pound load, the same gas spring may be used to support a load which is twice as large by increasing the internal pressure of the unit to substantially twice the pressure required to support the ten pound load.
Accordingly, provided other structural aspects of the gas springs are adequate to the task under consideration a number of load-bearing applications, or pre-load applying forces, may be satisfied by merely varying the amount of pressure or the charge level within the same spring unit.
Because of their simplicity, complete gas spring units may be manufactured and sold at relatively low cost. However, in spite of their known advantages, gas pressure spring units of the prior art have been capable of improvement in the seal area. In this connection, a practice in the prior art was to provide a multi-piece seal which required labor for assembly, and which was not as reliable as might be desired in operation.
Typically, prior art seals were made from perhaps three elements, and in some cases, as many as five separate elements In the five-piece seal, one element was a so called nosepiece which was used in forming the curl serving in use to partially close off the otherwise open end of the tube. Other elements included a felt wiper unit used as a dust wiper or dirt excluder, a separate part used to position the dust or dirt wiper in use, and a composite packing or seal unit used in actually providing the gas-tight seal. This was customarily itself a two-element part with a stiff backing ring and a seal element of V-shape in radial cross-section. These element seals included a nosepiece, a seal and a positioning ring.
Seal assemblies used in prior art gas springs also included a still further separate element in the form of a protecting ring which lay on the high pressure side of the seal assembly and which protected the seal itself and also contained a groove or like means for receiving a locking or crimping bead to prevent axial movement of the seal assembly as a whole.
In the prior art, it was found necessary to assemble the foregoing parts by hand, and then position them one-by-one within the open end of the tube, retaining them in this position during the changing step, and finally curling the ends, after which the unit as a whole would be tested.
Another characteristic of prior art assembled seals was that the seal retainer or protector unit lying on the axially innermost portion of the assembly also served as the "snubber" or movement limiting portion of the seal. This part of the seal, in other words, engaged the lower surface of the piston when the rod was fully extended. Hence, forces tending to urge the piston even further axially outwardly were resisted only by the strength of the crimp or other lock holding this protector unit against axial movement.
In the present invention, the seal is an integral unit and the forces acting on the piston may be transmitted directly from the axially inner or "snubber" end of the seal assembly to the end curl or the like on the opposite axial end of the housing. The seal of the present invention is retained against axial movement in the other direction by a bead, groove, or series of spaced apart dimples which need provide only small forces as necessary for this limited purpose.
In view of the prior art, there existed a need for an improved seal unit which would provide the advantages of the foregoing seals with lower cost and reduced complexity, and which would provide additional advantages as well.
Accordingly, it is an object of the present invention to provide an improved, one-piece seal assembly for a gas spring unit.
Another object is to provide a gas spring assembly having an improved seal forming a part thereof, and cooperating with a piston and rod assembly to seal gas pressure within the housing portion of the assembly.
A further object of the invention is to provide combination gas retention and rod wiper seal in a single unit, which seal may include the functions of providing a guide for the rod, and for providing a series of combination seal lips and check valves for facilitating charging of the gas pressure seal unit after assembly.
Another object of the invention is to provide a seal which includes a positioning body having an end portion which is base or optionally covered with elastomer so as to provide a snubber surface for engagement by the piston portion of the spring assembly to limit axial movement of the rod an piston and to transmit this force directly through the seal to the axially outer end thereof.
A still further object of the invention is to provide a seal wherein positioning may be achieved by an end curl and only a few dimples or a shallow-depth seal locating groove found in the housing portion of the unit.
Another object of the invention is to provide a novel seal assembly for this application, which seal assembly includes an integrally formed rigid one-piece positioning body associated in use with an elastomeric, multi-lip seal body.
Yet another object of the invention is to provide a seal assembly which includes a positioning body having an enlarged thickness portion having guide surfaces adjacent the inner diameter of one end thereof, and which includes a reduced thickness collar or the like serving as locating surfaces for the elastomeric seal body.
Another object of the invention is to provide a seal assembly which includes an elastomeric seal body providing not only a portion adapted to receive a dimples or other formations for locating the seal, but which also provides both a primary and a secondary or static lip seal, and which may additionally provide one or more auxiliary or excluder seal lips.
A further object of the invention is to provide a seal for a gas spring application wherein a primary seal lip and an excluder lip are both provided for engagement with the outer diameter surface of a reciprocable rod forming a part of the seal assembly and wherein both the seal lips act as check valves as well as pressure seals for a gas which is used to pressurize the spring unit after assembly.
A yet further object of the invention is to provide a spring which will provide the same or improved functions relative to prior art seals and which does so at reduced cost.
A still further object of the invention is to provide a seal which incorporates materials particularly suited to a gas spring application and which simplifies installation and handling of the seal.
Yet another object is to provide a seal design wherein the seal lip body may, but need not be, bonded to the positioning body.
The foregoing and other objects and advantages of the invention are achieved in practice by providing a one-piece multi-purpose seal unit which includes a positioning body and an elastomeric seal body, and wherein the seal body is affixed to a collar or reduced thickness portion of the positioning body so as to provide a radially outwardly static seal, at least one radially inwardly directed primary seal for engagement with the rod surface, and which further includes a snubber surface on one end portion for limiting piston travel, with one or more of the primary sealing lips being constructed and arranged so as to act as check valves to permit gas pressure to be added from the exterior of the unit to the interior thereof, and thereafter retaining such gas within the interior of the spring seal unit.
The manner in which the foregoing and other objects and advantages of the invention, including its inherent objects and advantages, are achieved practice will become more clearly apparent when reference is made to the accompanying detailed description of the preferred embodiment of the invention set forth by way of example, and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.